linux-kernel - Re: [PATCH 1/3] kexec_file: fix incorrect end value passed to kimage_is_destination

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Date: Fri, 15 Dec 2023 11:46:28 -0600
From: "Eric W. Biederman" <ebiederm@...ssion.com>
To: Yuntao Wang <ytcoode@...il.com>
Cc: linux-kernel@...r.kernel.org,  kexec@...ts.infradead.org,
  x86@...nel.org,  Andrew Morton <akpm@...ux-foundation.org>,  Thomas
 Gleixner <tglx@...utronix.de>,  Ingo Molnar <mingo@...hat.com>,  Borislav
 Petkov <bp@...en8.de>,  Dave Hansen <dave.hansen@...ux.intel.com>,  "H.
 Peter Anvin" <hpa@...or.com>,  Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH 1/3] kexec_file: fix incorrect end value passed to
 kimage_is_destination_range()

Yuntao Wang <ytcoode@...il.com> writes:

> The end parameter received by kimage_is_destination_range() should be the
> last valid byte address of the target memory segment plus 1. However, in
> the locate_mem_hole_bottom_up() and locate_mem_hole_top_down() functions,
> the corresponding value passed to kimage_is_destination_range() is the last
> valid byte address of the target memory segment, which is 1 less. Fix
> it.

If that is true we I think we should rather fix
kimage_is_destination_range.

Otherwise we run the risk of having areas whose end is not
representable, epecially on 32bit.

Eric

> Signed-off-by: Yuntao Wang <ytcoode@...il.com>
> ---
>  kernel/kexec_file.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index f9a419cd22d4..26be070d3bdd 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -435,13 +435,12 @@ static int locate_mem_hole_top_down(unsigned long start, unsigned long end,
>  		if (temp_start < start || temp_start < kbuf->buf_min)
>  			return 0;
>  
> -		temp_end = temp_start + kbuf->memsz - 1;
> -
>  		/*
>  		 * Make sure this does not conflict with any of existing
>  		 * segments
>  		 */
> -		if (kimage_is_destination_range(image, temp_start, temp_end)) {
> +		if (kimage_is_destination_range(image, temp_start,
> +						temp_start + kbuf->memsz)) {
>  			temp_start = temp_start - PAGE_SIZE;
>  			continue;
>  		}
> @@ -475,7 +474,7 @@ static int locate_mem_hole_bottom_up(unsigned long start, unsigned long end,
>  		 * Make sure this does not conflict with any of existing
>  		 * segments
>  		 */
> -		if (kimage_is_destination_range(image, temp_start, temp_end)) {
> +		if (kimage_is_destination_range(image, temp_start, temp_end + 1)) {
>  			temp_start = temp_start + PAGE_SIZE;
>  			continue;
>  		}